1. Field of the Invention
The present invention relates to an energy conversion device using rectifying antennae (“rectannae”). In particular, the present invention relates to an energy conversion device which converts electromagnetic wave energy to electrical energy using a semiconductor device that rectifies a small high frequency signal.
2. Discussion of the Related Art
FIG. 1 shows the current versus voltage characteristics of a conventional pn junction diode. FIG. 2 is a schematic representation of conventional abrupt pn junction diode 100. As shown in FIG. 2, conventional pn junction diode 100 includes p-region 101 and n-region 102. P-region 101 may be doped, for example, using a p-type dopant (i.e., electron acceptor, such as boron) and n-region 102 may be doped using an n-type dopant (i.e., an electron donor, such as phosphorus). Near the abrupt junction between p-region 101 and n-region 102, equilibrium due to the difference in electrochemical potentials of the two regions and the diffusion of charge carriers (e.g., electrons and “holes”) between the two regions deplete the charge carriers to form “depletion regions” 103 and 104 in p-region 101 and n-region 102, respectively. Under a so-called “abrupt junction approximation”, the widths xp of depletion region 103 and xn for depletion region 104, with an externally imposed voltage V across the pn junction, are given, respectively by:
            x      n        =                            2          ⁢                                          ⁢                      ɛ            s                    ⁢                                    N              A                        ⁡                          (                                                ϕ                  i                                -                V                            )                                                            qN            D                    ⁡                      (                                          N                A                            +                              N                D                                      )                                          x      p        =                            2          ⁢                                          ⁢                      ɛ            s                    ⁢                                    N              D                        ⁡                          (                                                ϕ                  i                                -                V                            )                                                            qN            A                    ⁡                      (                                          N                A                            +                              N                D                                      )                              where εs is the electrical permittivity of silicon, q is the charge of an electron, φi is the “built-in” potential of the pn junction, NA and NB are the doping concentrations of p-region 101 and n-region 102, respectively.
As shown in FIG. 1, the horizontal axis shows the voltage V across the pn junction, and the vertical axis shows the diode current ID across the pn junction. As shown in FIG. 1, when voltage V across the pn junction is greater than zero volts and greater than voltage Vth (the “threshold voltage”), the pn junction is strongly “forward biased” and the diode current ID grows exponentially with the voltage V. When the voltage V across the pn junction is less than 0 volts, but not less than the voltage Vbr (the “breakdown voltage”), the pn junction is “reverse biased” and the diode current ID is very small. Under reversed bias, as the voltage grows in magnitude, the carriers generated increases in energy, leading to phenomena such as tunneling and impact ionization at voltage Vbr. At voltage Vbr, the diode current ID becomes very large and the diode has “broken down.” At breakdown, the magnitude of the average electrical field (in volts per centimeter) across the pn junction is given by the empirical expression:
                E      br            =            4.0      ×              10        5                    1      -                        1          3                ⁢        log        ⁢                              N            D                                10            16                              where ND is the lesser of NA and NB.